1. Field of the Invention:
The invention relates to an infinitely variable traction roller transmission having motion transmitting traction rollers disposed between, and in engagement with, opposite toric discs mounted on input and output shafts.
2. Description of the Prior Art:
Ratio control of such a transmission is obtained by applying to the traction rollers forces which provide a precess movement that causes pivoting of the support structure of the traction rollers in order to provide for different circles of engagement of the traction rollers with the toric input and output discs with which they are engaged. Such transmissions are described in detail in this applicants U.S. Pat. Nos. 4,275,610; 4,086,820; and 3,810,398 and earlier application Ser. No. 168,521.
Control of high power infinitely variable traction roller transmissions has always been problematic because freedom must be provided for the traction rollers to permit precess movement thereof to initiate a change of the transmission ratio and because there are, during operation of the transmission, reaction forces applied to the traction rollers, which forces are in the precess movement direction of the traction rollers. Earlier designs are provided with cam structures to which the precess forces are applied, for example by a hydraulic piston, and which provide for a predetermined position of such piston for each transmission ratio.
The precess forces however are quite large because, at the same time, the transmission reaction forces must be accommodated and the cams and cam rollers are therefore subject to wear and, in any case, need to be of great strength. The resulting designs are therefore quite expensive.